1. Field of the Invention
This invention relates to a storage control technique for controlling the transmission of data between host systems and a storage apparatus including hard disks.
2. Description of Related Art
Storage controllers with the above technique control the migration of data between host systems and storage apparatuses based on data write/read requests sent from the host systems to the storage apparatuses. They also provide the storage areas in the storage apparatuses, as logical areas, to the host systems. The host systems access logical volumes and write/read data to/from the logical areas in the logical volumes. The storage controllers are also called storage subsystems and they constitute, with the host systems, storage systems. Each storage apparatus includes a plurality of storage devices, e.g., hard disk drives.
With the increase in the amount of data handled in host systems, the volume size—storage capacity of logical volumes—has to be proportionate to that amount. If large-size logical volumes are allocated to host systems in the first place, there will be no shortage of storage capacity for the host systems. However, if the host systems do not handle a large amount of data, there will be unused areas in the storage areas allocated to the host systems, which means that the storage resources are wasted.
JP2005-11316 A discloses a storage area allocated to a volume for the first time when a processor in a host computer write-accesses the volume. U.S. Pat. No. 6,823,442 describes volumes host systems access provided in a storage system and physical storage areas allocated to these volumes.
Incidentally, as a relevant conventional example, JP2005-128771 A describes a data file system having: a data access server that has a data-storing physical storage device accessed in response to an access request; and a data file server that sends an access request to the data access server and performs data filing using the data access server to store data. In this data file system, when a logical block is no longer used, its physical block is released.
JP2004-127301 A describes a storage system having: virtual storage spaces; physical storage spaces; a mapping system that associates the addresses of the virtual storage spaces with the addresses of the physical storage spaces; and a controller that automatically deletes a portion in the mapping system in accordance with the priority rule for designating deletion target portions in the mapping system. JP2005-234820 also describes a technique related to this invention.
The inventors of this invention have developed a technique called Allocation-on-Use (AOU) for the effective use of storage resources in a storage system. A storage controller provides virtual volumes—volumes without actual storage areas—to host systems and establishes correspondences between the virtual volumes and the logical volumes called pools—volumes to which real storage areas in the storage apparatus are allocated. When a host systems write-accesses an area in a virtual volume, the storage controller allocates a storage area in a pool volume to the host-accessed area in the virtual volume. Allocation is performed each time any of the host systems writes new data in any of the virtual volumes. The host systems only see the virtual volumes with a seemingly large storage capacity. Because the storage controller does not allocate large-capacity storage areas to the host systems from the beginning, but allocates a storage area on each occasion, the host systems can use the storage resources in the storage apparatus effectively.
When a host system deletes data, if it deletes not the data itself but only the management information for the data, the storage controller cannot recognize the storage areas storing unnecessary data and these storage areas remain in the storage apparatus, running the risk that they accumulate in the storage apparatus, which prevents the host systems from using the storage resources in the storage apparatus effectively.
This invention aims to provide a storage control technique by which, although actual data is not deleted but the management information for that data is deleted, a host system can recognize the storage areas storing unnecessary data, and accordingly use them effectively.
Another object of this invention is to provide a storage control technique by which the storage areas storing unnecessary data are released from allocation to the host systems so that they can be used by the host systems effectively. Still another object of this invention is to provide a storage controller and storage control method that enable the effective use of the storage resources in the foregoing AOU storage systems.